The recent publicity and emphasis on the "information superhighway" has increased awareness and acceptance of the Internet as a mass communication media. This broad based recognition of the Internet as a viable media for communication and interaction across multiple networks has also created a large established user base built upon the Internet standardized protocols for interaction between computer networks.
The paradigm for the Internet is that of a client-server relationship where Internet clients (browsers) communicate with Internet servers. To provide greater access to the Internet, the communication protocols and languages utilized by the clients and servers have become standardized. These protocols include the Hyper-Text Transfer Protocol (HTTP), which is the communication protocol used for communications between clients and servers, and the Transfer Control Protocol/Internet Protocol (TCP/IP). The TCP portion is the transport-specific protocol for communication between computers or applications. IP is a lower-level protocol than TCP and facilitates the transmission of data packets between remotely-located machines. TCP is a transport-level protocol that operates on top of IP. TCP provides a full-duplex byte stream between applications, whether they reside on the same machine or on remotely-located machines. TCP ensures that transmitted data packets are received in the same order in which they were transmitted.
TCP is a connection-oriented reliable transport protocol layered over IP. Each TCP connection maintains information about a connection's state in a data structure called a Transmission Control Block (TCB). In addition to information about a connection's state, a TCB typically also contains various other connection information, as is known to those skilled in the art. When a server actively closes a TCP connection with a client, the TCB associated with the connection is maintained by the server for a period of time, referred to as "TIME-WAIT" state. The length of time a closed connection remains in TIME-WAIT state is typically two times the maximum segment lifetime (MSL). By definition a MSL is equivalent to thirty seconds. The server must, as a result, allocate resources for each closed connection for a period of one minute. Busy servers often have connection tables full of closed connections in TIME-WAIT state. As connection tables fill up with closed connections in TIME-WAIT state, room for new connections often becomes unavailable. As a result, server performance suffers and fewer client connections can be established with the server until connections in TIME-WAIT state are purged or aged.
Another characteristic of TCP is a technique referred to as "slow-start." TCP does not fully utilize available network bandwidth for the first few round-trips of a connection between a client and a server. Slow-start is a network congestion avoidance mechanism which is employed when a client-server connection is established, a packet is lost or long network delays occur. Slow-start initially allows the sender to send only one packet. For each acknowledgement that is received, the number of packets that the sender is allowed to transmit is increased by one.
In slow-start, a both ends of a connection maintain a window of unacknowledged packets called the congestion window. When a connection starts up, each sender is only allowed to have a single unacknowledged packet in transit. When an acknowledgement is received, the congestion window is incremented from one to two, and two packets can be sent. When each of those two packets is acknowledged, the congestion window is increased to four. The window is opened gradually, doubling the number of data packets each round-trip time. As is known to those having skill in the art, TCP achieves full throughput first when the effective window size is at least the product of the round-trip delay and the available network bandwidth. Although slow-start is advantageous for avoiding network congestion, it degrades server performance when many short-lived connections are made.
In the context of World Wide Web ("web") client/server applications, the client may be a web browser which acts as the user interface. The web browser sends user requests to the appropriate web server and formats and displays the HTML data returned from the web server. The web browser also evaluates the HTML data to determine if there are any embedded hyper-link statements in the HTML data which would require subsequent browser requests which would then be initiated by the browser. A web server acts as the server for the client and processes a web browser's requests and returns the requested response as an HTML data portion of a HTTP data stream. Thus, it is possible for a Web server to have repeated connections to the same client over a short period of time.